Weather radars, such as found on aircraft or marine vessels, display hazardous weather information based upon analyzed radar returns. Radar return information corresponding to detected hazardous weather information is presented to the crew of the aircraft or marine vessel on a display, typically using a plan view showing a geographic area over which the aircraft or vessel is traversing.
However, weather radars have a limited effective range. At the farther extents of the range of the weather radar, the weather radar system has difficulty distinguishing between weather radar returns and terrain radar returns. This difficulty relates to weather and terrain being close to each. Thus, an emitted radar signal may be incident on both weather and terrain. Accordingly, the weather radar system may receive return signals from both the weather and the terrain.
For example, an aircraft at cruising altitude over Kansas may have an effective radar range of about 300 nautical miles based upon the curvature of the earth and the signal strength of the returned radar signal. This effective range of the onboard radar may be referred to as the radar horizon. However, at the far extent of this range, the onboard radar may have difficulties distinguishing between valid weather radar returns and terrain radar returns, such as radar returns caused by mountains. Here, the vertical coverage range of an emitted radar signal is relatively large at the radar horizon. Accordingly, the weather radar system may receive return signals from both the weather and the terrain.
In some situations, the radar range can be limited, or blocked, by terrain. For example, the effective range of the weather radar will be significantly reduced when mountain ranges block the emitted radar signals. As another example, if a marine vessel is sailing around a point or peninsula with mountains, the marine vessel's weather radar would not be able to detect weather on the far side of the point or peninsula. Here, the onboard radar system cannot see “over” the mountains. Further, it may be difficult for the weather radar system to distinguish between radar returns from the mountain peaks and weather radar returns caused by weather that is on, or just behind, the mountain peaks. In such situations, the weather radar system may receive return signals from both the weather and the terrain.
In yet other situations, the radar range can be limited by a low altitude of the aircraft. When an aircraft is taking off or landing, the low altitude of the aircraft will result in a limited radar range since the earth horizon is relatively close to the aircraft (as compared to the far range of the earth horizon when the aircraft is at cruising altitude). Thus, it may be difficult to identify radar returns caused by weather which lies along the relatively close-range earth horizon. Accordingly, the weather radar system may receive return signals from both the weather and the terrain. Further, lower elevation weather is not detectable since it lies below the earth horizon during takeoff or landing.
Accordingly, the weather radar may not be able to reliably differentiate between weather radar returns and terrain radar returns along the radar horizon of the weather radar. Accordingly, it is desirable to improve the ability to differentiate between weather radar returns and terrain radar returns along the radar horizon of an aircraft's or marine vessel's weather radar so that the crew of the aircraft or vessel have more time to respond to adverse weather conditions.